Merge branch 'improve-mr-reloading' into 'master'

Improve MR reloading

## Theory

Every time you pushed to master it updates merge requests that has master
as target branch. So if you have 50 open merge requests point to master
it will reload all of them every time you push a single commit to
master. The funny thing is that after reloading diff of most merge
requests looks the same.

After this patch we update diff only if we push commit to master that
includes in MR commits list.

For example we have next repository:

    feature: A - B - C
    master: A

We create merge request with code from feature to master.

    MR: B - C

If we push to master commit D - MR will not be reloaded. So picture will
look next:

    feature: A - B - C
    master: A - D
    MR: B - C

And if we push to master commit B - MR will be reloaded. So picture will
look next:

    feature: A - B - C
    master: A - B
    MR: C

## Benchmark

For project with 45 open merge requests to master

Before

```
Benchmark post-receive | Cache and size:   0.060000   0.040000   0.100000 (  0.379720)
Benchmark post-receive | Push commits selection:   0.130000   0.020000   0.150000 (  0.149299)
Benchmark post-receive | Update merge requests:   9.180000   2.030000  11.210000 ( 11.971747)
Benchmark post-receive | Process commit messages:   0.140000   0.010000   0.150000 (  0.168810)
Benchmark post-receive | Push data:   0.020000   0.000000   0.020000 (  0.016363)
Benchmark post-receive | Push event and services:   0.030000   0.000000   0.030000 (  0.088062)
```

After

```
Benchmark post-receive | Cache and size:   0.070000   0.030000   0.100000 (  0.106676)
Benchmark post-receive | Push commits selection:   0.130000   0.020000   0.150000 (  0.143081)
Benchmark post-receive | Update merge requests:   0.660000   0.210000   0.870000 (  0.892663)
Benchmark post-receive | Process commit messages:   0.030000   0.000000   0.030000 (  0.029263)
Benchmark post-receive | Push data:   0.020000   0.000000   0.020000 (  0.018479)
Benchmark post-receive | Push event and services:   0.030000   0.000000   0.030000 (  0.038230)
```
- - -

## References

Discussion in gitlab/gitlabhq#1796

See merge request !1288

3 files changed, 37 insertions, 10 deletions

diff --git a/app/services/merge_requests/refresh_service.rb b/app/services/merge_requests/refresh_service.rb
index 74448998ddd..baf0936cc3d 100644
--- a/app/services/merge_requests/refresh_service.rb
+++ b/app/services/merge_requests/refresh_service.rb
@@ -3,6 +3,7 @@ module MergeRequests
     def execute(oldrev, newrev, ref)
       return true unless ref =~ /heads/
 
+      @oldrev, @newrev = oldrev, newrev
       @branch_name = ref.gsub("refs/heads/", "")
       @fork_merge_requests = @project.fork_merge_requests.opened
       @commits = @project.repository.commits_between(oldrev, newrev)
@@ -35,6 +36,10 @@ module MergeRequests
       end
     end
 
+    def force_push?
+      Gitlab::ForcePushCheck.force_push?(@project, @oldrev, @newrev)
+    end
+
     # Refresh merge request diff if we push to source or target branch of merge request
     # Note: we should update merge requests from forks too
     def reload_merge_requests
@@ -43,8 +48,22 @@ module MergeRequests
       merge_requests = filter_merge_requests(merge_requests)
 
       merge_requests.each do |merge_request|
-        merge_request.reload_code
-        merge_request.mark_as_unchecked
+
+        if merge_request.source_branch == @branch_name || force_push?
+          merge_request.reload_code
+          merge_request.mark_as_unchecked
+        else
+          mr_commit_ids = merge_request.commits.map(&:id)
+          push_commit_ids = @commits.map(&:id)
+          matches = mr_commit_ids & push_commit_ids
+
+          if matches.any?
+            merge_request.reload_code
+            merge_request.mark_as_unchecked
+          else
+            merge_request.mark_as_unchecked
+          end
+        end
       end
     end
 
diff --git a/lib/gitlab/force_push_check.rb b/lib/gitlab/force_push_check.rb
new file mode 100644
index 00000000000..6a52cdba608
--- /dev/null
+++ b/lib/gitlab/force_push_check.rb
@@ -0,0 +1,15 @@
+module Gitlab
+  class ForcePushCheck
+    def self.force_push?(project, oldrev, newrev)
+      return false if project.empty_repo?
+
+      if oldrev != Gitlab::Git::BLANK_SHA && newrev != Gitlab::Git::BLANK_SHA
+        missed_refs = IO.popen(%W(git --git-dir=#{project.repository.path_to_repo} rev-list #{oldrev} ^#{newrev})).read
+        missed_refs.split("\n").size > 0
+      else
+        false
+      end
+    end
+  end
+end
+
diff --git a/lib/gitlab/git_access.rb b/lib/gitlab/git_access.rb
index 5f8cb19efdf..8b4729896b5 100644
--- a/lib/gitlab/git_access.rb
+++ b/lib/gitlab/git_access.rb
@@ -94,14 +94,7 @@ module Gitlab
     end
 
     def forced_push?(project, oldrev, newrev)
-      return false if project.empty_repo?
-
-      if oldrev != Gitlab::Git::BLANK_SHA && newrev != Gitlab::Git::BLANK_SHA
-        missed_refs = IO.popen(%W(git --git-dir=#{project.repository.path_to_repo} rev-list #{oldrev} ^#{newrev})).read
-        missed_refs.split("\n").size > 0
-      else
-        false
-      end
+      Gitlab::ForcePushCheck.force_push?(project, oldrev, newrev)
     end
 
     private